look up "ghost" canyoneering techniques... I would trust some much less than others. Probably the safest is to use a sling or piece of webbing with 2 links/rap rings/carabiners, use this to sling a tree and tie a pull cord to one of the rings/links/biners. run your rope through both rings/links/biners. At the bottom pull your rope and then use the pull cord to retrieve your anchor that was slung around a tree or something else. Or spend the 3-4 dollars and get some webbing and a few quick links that fit your rope.

Step 1- stack two nuts Step 2- rig single strand rappel off the brown nut(downward pull nut) Step 3- rig pull strand on the pushed through cable of the upside down nut Step 4- make peace with god and tell your partner to apologise to your family for you stupidity Step 5- rappel "safely" to the ground or your next belay Step 6- pull retrieval line and the nut on the right pulls out and your whole kit falls to the ground

Ive used a slightly advanced trick, similar to the nut trick that involves a cam, and is highly not recommended. It's been discusses at length before, but its worked twice for me. Same disclaimers as the nut trick about apologizing to your family apply.

I DO NOT ADVOCATE ANY OF THE FOLLOWING TECHNIQUES, FOR ANYONE, BEGINNER OR EXPERT ALIKE.

The basics of it are this:

FIRST, DO NOT USE THIS TECHNIQUE (my disclaimer)

Set your cam in a parallel or slightly, very slightly outward flaring crack.

Clove the halfway point of your rope to the cam stem itself so it is loading the cam when pulling on it.

Take a runner and weave it through the trigger bar of the cam so it can pull the bar as necessary to release the lobes.

Pull up a bit of slack on one side of the rope and clove it to the sling.

Rap on the single line, and only that line, loading the cam.

Get down and pull hard and quick on the line attached to the trigger.

A side note, the looks on people's faces when they realize exactly how this works when I've explained it in person are priceless.

Buff, there's a similar method that arborists use when they install/remove a cambium saver sling. It involves a sling (I suppose you could make one using cord) with a small ring at one end and a large ring at the other. When the rope is doubled through both rings, a knot can be tied on the leg of the rope on the side of the large ring. pull the other leg of rope and the knot will slide through the large ring and catch the small ring, then the whole assembly comes down. Premade slings are available from various arborist suppliers. The process is also described in the Jeff Jepsom book, "The Tree Climbers Companion, 2nd edition". the beauty of it is, you would not need a tag line, but it would likely take a small bit of practice to figure out what knot you needed to tie to retrieve the setup.

Here's a link to the slings I described above, and there is a picture there with a small illustration of how it's installed/removed from the ground. Obviously, the removal is the important thing in the rock climbing context.